Video Transcript
According to Arrhenius theory,
which of the following can an acid be defined as? (A) A substance that changes the
color of an aqueous solution. (B) A substance that ionizes in an
aqueous solution to produce OH− ions. (C) A substance that fizzes when
placed into an aqueous solution. (D) A substance that dissolves any
substance placed into a solution of it. (E) A substance that ionizes in an
aqueous solution to produce H+ ions.
To solve this problem, we need to
carefully read through each answer choice to determine if it is an accurate
definition of an acid. The definition of the acid must
correspond to the Arrhenius theory of acids and bases. This theory, proposed by Swedish
scientist Svante Arrhenius in 1887, focused specifically on how acids and bases
ionize or dissociate into ions when dissolved in water. The result of an acid or base
ionizing in water is an aqueous solution containing dissolved ions. Let’s begin examining the answer
choices.
The statement in answer choice (A)
describes the substance that changes the color of an aqueous solution. Arrhenius theory defines an acid
based on the ability of the acid to ionize in an aqueous solution, not change the
color of the solution. Because ionization is not
described, answer choice (A) can be eliminated. Next, let’s take a look at answer
choice (C). This statement describes a
substance that fizzes when placed into an aqueous solution. The Arrhenius definition of an acid
must include how an acid ionizes when dissolved in water. Because ionization is not
described, answer choice (C) can also be eliminated.
The statement in answer choice (D)
describes a substance in a solution that will dissolve any substance placed into
it. It’s important to recognize that
Arrhenius theory is focused on what happens when an acid dissolves in water, not
what happens when substances are dissolved in an acidic solution. We can eliminate answer choice (D)
for this reason. And there are plenty of examples of
substances that will not dissolve in an acidic solution.
The only answer choices left our
answer choices (B) and (E). Both of these answer choices
describe a substance that ionizes in an aqueous solution, but only one of them is
correct. The substance in answer choice (B)
produces OH− ions when it ionizes in the solution. This statement is the definition of
a base according to Arrhenius theory. An example of an Arrhenius base is
potassium hydroxide or KOH. When solid potassium hydroxide
dissolves in water, it ionizes to produce K+ and OH− ions in the solution. We can eliminate answer choice (B)
because the statement is the definition of a base.
Finally, answer choice (E)
describes a substance that ionizes in an aqueous solution to produce H+ ions. This statement is the definition of
an acid according to the Arrhenius theory. An example of an Arrhenius acid is
hydrobromic acid or HBr. When dissolved in an aqueous
solution, hydrobromic acid molecules ionize to produce H+ and Br− ions. The hydrogen ions produced are then
accepted by water molecules in the aqueous solution forming H3O+ or hydronium
ions.
The statement that defines an acid
according to the Arrhenius theory is answer choice (E), a substance that ionizes in
an aqueous solution to produce H+ ions.